Shared Risk Group (SRG) is a concept in network routing that different connections may suffer from a common failure if they share a common risk or a common SRG. SRG can also be used with optical networks, Ethernet networks, Multiprotocol Label Switching (MPLS) networks including the Generalized Multiprotocol Label Switching (GMPLS) networks, Internet Protocol (IP) networks, and the like as well as multi-layer networks with any of the foregoing. An SRG failure makes multiple connections go down because of the failure of a common resource those connections share. Examples of SRGs include Shared Risk Link Group (SRLG), Shared Risk Node Group (SRNG), Shared Risk Equipment Group (SREG), etc. The descriptions herein reference SRLGs, but those skilled in the art will recognize any type of SGR risk representation is contemplated herein. SRLGs refer to situations where links in a network share a common fiber (or a common physical attribute such as fiber conduit or the like). If one link fails, other links in the group may fail too, i.e., links in the group have a shared risk which is represented by the SRLG. SRLGs are used in optical, Ethernet, MPLS, GMPLS and/or IP networks and used for route computation for diversity. In multi-layer networks, a link at upper layer represents a connection at lower layer and thus any network resources (links, nodes, line cards, and the like) used by the lower layer connection can be represented as SRLGs on the upper layer links. For example, an MPLS link at MPLS layer may represent a connection at Layer 0 and thus any ROADM nodes, amplifiers, and muxing/demuxing components as well as fiber cables and conduits used by the Layer 0 connection can be represented as SRLGs on the MPLS link. It is thus possible that links have a large number of SRLGs assigned and thus an efficient representation of SRLGs is highly desirable, both for storage, dissemination (flooding) as well as path diversity computation purposes.
Conventionally, each specific SRLG is a unique 32-bit number (or some other large number) that is assigned against associated links in a network. For diversity route computation, the process of checking for diversity includes sorting all of the SRLGs between each link for comparison and checking if any of the same SRLG is present. The absence of SRLGs between links indicates no common failures. If a particular link has four SRLGs, that link has four 32-bit numbers associated with it (i.e., flooded in advertisements, stored at network elements, used in diversity route computation, etc.). This becomes particularly complex and unmanageable in multi-layer networks. For example, assume 20 SRLGs per link at Layer 0 (photonic layer) in a network and 20 links for a Layer 0 connection, there could be 400+ SRLGs to track for the Layer 0 connection. Assume a higher layer protocol, e.g., MPLS, operates on the Layer 0 network. There is a finite number of SRLGs for the higher layer protocol, e.g., 32, 40, etc. that can be tracked for each MPLS link. It may not be possible to track all of the SRLGs of the Layer 0 connection when such connection at Layer 0 represents an MPLS link at MPLS layer. Conventional approaches here include prioritizing the SRLGs at the higher layer protocol and ignoring less important SRLGs (e.g., not assigning them) from lower layers. However, as networks continue to scale and management of these networks is performed on a multi-layer fashion, this approach does not work.
There are techniques for compressing SRLGs such as the Macro SRLG technique (see Request for Comments (RFC) 7926, Appendix B.1, July 2016, the contents of which are incorporated herein) which stipulates that an SRLG representing a particular network risk need only be assigned against a link if two or more such links make use of such network risk. When upper-layer links sparsely use the underlying network (L0) infrastructure then Macro SRLGs would offer good summarization capabilities but as more and more upper-layer links are added on top of network (L0) infrastructure then the chances are high that two or more such upper-layer links will use a particular network risk and thus a large number of SRLGs representing these network risks would need to be assigned to the links.
Again, based on network scaling and the management of multi-layer networks, there is a need for efficient SRLG representations.